Anti-skid control system for a rear drive vehicle

Abstract

The invention is directed to an arrangement for controlling a braking force applied to each of road wheels of a rear drive vehicle depending upon a braking condition, with a hydraulic braking pressure supplied to each of wheel brake cylinders through pressure control valves respectively. The pressure control valves are controlled by the braking force controller into which output signals of wheel speed sensors are fed. In a first determination unit, it is determined if at least one of the front road wheels is on a road surface of a coefficient of friction lower than a predetermined value, and determined if the front wheel speed of one of the front road wheels has reached to a peak wheel speed. And, in a second determination unit, it is determined if a difference between the front wheel speed and rear wheel speed is less than a predetermined speed. When it is determined that at least one of the front road wheels is on the road surface of the low coefficient of friction and the front wheel speed has reached to the peak wheel speed, and that the difference between the front and rear wheel speeds is less than the predetermined speed, an asynchronous control unit prohibits the braking force controller from synchronously controlling the braking force applied to the front road wheels.

What is claimed is: 
     
       1. An anti-skid control system for controlling a braking force applied to road wheels of an automotive vehicle for driving right and left road wheels at a rear side of said vehicle, comprising: wheel brake cylinders operatively connected to right and left road wheels, respectively, at front and rear sides of said vehicle for applying braking force thereto;   a hydraulic pressure generator for supplying a hydraulic braking pressure to each of said wheel brake cylinders;   actuating means disposed in each hydraulic circuit communicating said hydraulic pressure generator with each of said wheel brake cylinders for individually controlling the hydraulic braking pressure in each of said wheel brake cylinders;   wheel speed detecting means for detecting a front wheel speed of each of said front road wheels and a rear wheel speed representative of wheel speeds of said rear road wheels, and providing output signals corresponding to said front wheel speed and rear wheel speed;   braking force control means for controlling said actuating means in response to said output signal of said wheel speed detecting means to control the braking force applied to said road wheels;   first determination means for determining if at least one of said front road wheels is on a road surface of a coefficient of friction lower than a predetermined value and determining if the front wheel speed of one of said front road wheels has reached to a peak wheel speed;   second determination means for determining if a difference between said front wheel speed and said rear wheel speed is less than a predetermined speed; and   asynchronous control means for prohibiting said braking force control means from synchronously controlling the braking force applied to said front road wheels, when said first determination means determines that at least one of said front road wheels is on a road surface of the coefficient of friction lower than the predetermined value and that the wheel speed of one of said front road wheels has reached to the peak wheel speed, and said second determination means determines that a difference between said front wheel speed and said rear wheel speed is less than the predetermined speed.   
     
     
       2. An anti-skid control system according to claim 1, wherein said asynchronous control means makes said braking force control means to control said actuating means to hold the hydraulic braking pressure in the wheel brake cylinder operatively connected to one of said front road wheels, until said actuating means terminates increasing the hydraulic braking pressure in the wheel brake cylinder operatively connected to the other of said front road wheels. 
     
     
       3. An anti-skid control system according to claim 1, wherein said rear wheel speed is an average of the wheel speeds of said rear road wheels. 
     
     
       4. An anti-skid control system according to claim 1, wherein said rear wheel speed is a rotational speed of an axle of said rear road wheels.